Underground fuel storage tanks are required by law to prevent liquid leaks below ground to avoid soil and groundwater contamination. To meet this requirement, tanks conventionally include a water tight sump shield assembly that collects any fuel leakage from pipes, valves, or other equipment at the upper part of the tank. Sensors and alarms are also provided as an alert to such condition. Water that enters the sump, for alarmed base sumps, is occasionally falsely sensed as a fuel leak, requiring immediate examination and corrective action.
It is known in the art that the covers for sump assemblies cannot remain properly sealed against rain and other water runoff. Such runoff seeks the lowest level and can enter the sump assembly. This water when mixed with the aforementioned fuel leakage also creates a contaminated condition that must be dealt with promptly. This condition wastes much time and effort, and, therefore, expense to deal with recurring contamination. More seriously, as described below, the cover sealing problem becomes worse over time to the point when the sump can fill completely with water run-off and fuel mixture. This can lead to an overflow of fuel-contaminated water that can contaminate surrounding soil often leading to fines, contamination clean-up, and the expense of digging up the concrete-imbedded leaking assembly and replacing it with a new sump assembly and concrete.
The principal cause of the above problems stems from the standard sump covers, which do not provide a seal strong or reliable enough to prevent water from entering the containment sump. Weak cover seals can result from poor design, poor installation, poor materials, and the like.
Many sumps are made of polyethylene or other plastics. Cover leakage also results from installed or migrating back fill or concrete, which initially or over time, compresses the sump into an egg-shape or other distortion. The plastic under constant pressure tends to flow and distort causing the distorted sump opening lip to breech the circular, metal cover seal.
Sump assembly manufacturers have tried to overcome these problems, such as providing a unit that seals on the inside surface of the sump by means of an expandable plug design. Unfortunately, each unit needs to be customized to fit a particular design criterion, such as size of the collar opening, etc. If the unit distorts in the field, then the operator must wait until a new plug is manufactured to the new dimensions, which may result in fines, shut-down, or contamination. Thus, customizing for each unit increases the costs of the product and requires complex and delayed supply practices.
Another commercial unit relies on epoxies or other adhesives to seal the cover to the collar lip. Bonding materials compatible with polyethylene have only recently been introduced to the market. But these materials are not compatible with fuel hydrocarbons and may themselves contaminate the fuel being pumped or stored.
Accordingly, there is a need for a fuel storage containment sump shield assembly that provides a watertight seal over a long period of time to prevent water from entering the containment sump assembly for underground fuel storage tanks.